1. Field of the Invention
This invention relates to display systems, and more particularly to raster scan display systems having a rotatable CRT.
2. Description of the Prior Art
Rotation is a known technique with stroke displays which enables the system to display the text page outline in either of the two orientations. On a stroke display or gas panel display this rotation is not unreasonably difficult since both displays may be addressed with an X-Y coordinate and rotating the display implies simply interchanging X and Y. However, this is not true for a typical raster scan display.
The raster technique is used in most video display monitors and in virtually all television receivers. As the name implies, the electron beam scans the raster at a fixed rate, normally, left to right and top to bottom. This is known as horizontal scanning. Vertical scanning, on the other hand implies scanning from bottom to top and left to right.
Displaying textual data on a raster monitor is a well known technique where the character is sliced into pieces of video bits which are displayed on adjacent scan lines. In a progressively scanned system, the electron beam traces the characters by rows in ascending order. The rows are of a fixed length determined by the width of the display screen and the number of text lines is fixed by the height of the display screen. Since display screens are rectangular in shape it becomes desirable to rotate the display such that the vertical side is longer for displaying longer documents such as legal size documents, or such that the horizontal side is longer for displaying extra wide documents. Rotation of the display replaces horizontal scanning with vertical scanning where the yoke is rotated, or vice versa. For fixed pitch characters, vertical scanning is not more difficult than horizontal scanning. However, proportionally spaced characters are much more complex with vertical scanning because the characters on adjacent lines do not line up. This implies that text pointers are needed for each line of text and that the information throughput of the character generator is less. Further since both horizontal and vertical scanning are required there is the attendant cost of dual implementation.